NASA CR- /7

(NASA-CR-114685) THE DEVELOPMENT OF AN N74-12784ELASTIC REVERBS GRADIENT GaRMENT TO BEUSED AS A COUNTERMEASUEE FORCARDIOVASCULAR DECONDITIONING (Webb Unclas

Associates) 69 p HC CSCL C6B G3/n5 2 48

THE DEVELOPMENT OF AN ELASTIC REVERSE GRADIENT GARMENT

TO BE USED AS A COUNTERMEASURE

FOR CARDIOVASCULAR DECONDITIONING

by James F. Annis and Paul Webb

Distribution of this report is provided in the interest ofinformation exchange. Responsibility for the contents

resides in the author or organization that prepared it.

Prepared under Contract No. NAS2-7156 by

WEBB ASSOCIATES, Inc.Yellow Springs, Ohio

for

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

Reproduced by

NATIONAL TECHNICALINFORMATION SERVICE

US Department of Commerce bSpringfield, VA. 22151

TABLE OF CONTENTSpage

Summary 1

Introduction 2

Physiological Aspects of Cardiovascular Deconditioning 3

Deconditioning Countermeasures 4

History and Background 4

Principle of Operation 6

The RGG System 8Description of the Garments 8Breathing System and Pressurization Schedule 14

Breathing System 14Pressurization Schedule 14

Helmet and Bladder Assembly 18

Garment Design and Construction Methods 21Fabrics 21Subjects and Measurements 23

Selection 23Measurements 23

Fabric Engineering 25

Accessory Equipment and Methods 33Counterpressure Measurement Device 33Venous Compliance Measurement 34.

Treatment Methods 35

Results of Treatment Related Measurements 39Electrocardiographs and Heart Rate 39Venous Compliance 42Tests of Garment Function 42

Discussion 44

Appendix A: Rationale for a Dynamic Treatment Regimewith the Reverse Gradient Garment 47

Appendix B: Development of an Improved Power-Net Fabricfor Use in a Reverse Gradient Garment 50

Appendix C: Physical Properties of the 100% Nomex Fabric(non-stretch) Used in RGG Construction 61

PR-C NG PA" LAN NOT FLE

iii.

Appendix D: Computer Program: Fabric "cut-lengths" tosupply a given counterpressure for a range ofcircumferences 62

Appendix E: List of Tests Performed on Subjects 63

References 64

LIST OF FIGURES

Fig. # page1 Line drawing of the slip layer girdle 8

2 Photograph of subject wearing slip layer girdle 9

3 Line drawing of the slip layer top 10

4 Photograph of subject wearing complete slip layer 11

5 Line drawing of the outer full-body garment 13

6 Photograph of subject wearing full RGG assembly 13

7 Arrangement of the breathing system components 14

8 Sketch of the pressure regulating componentsof the breathing system 16

9 Curve showing the profile of the pressure scheduleused during the RGG treatments 17

10 Photograph of one of the full bubble helmets 18

11 Cross-sectional view of the helmet 19

12 Sketch showing the position and coverage of the torsopressurizing-breathing bladder & supplementary bladders 20

13 Stress-strain or power curves for the elastic fabric 28

14 Reproduction of a working layout leg pattern for the RGG 30

15 Pressurization scheme of the complete RGG system 32

16 Internal detail of the garment counterpressure sensor 33

17 Effect of breathing pressure on heart rate 41

18 Venous compliance change over 15 days of bed rest 43

iv.

LIST OF TABLES

pageTable 1. Basic Physical Characteristics of the Subjects 23

Table 2. Selected Anthropometric Measurements of theTreated Subjects 26-27

Table 3. Daily Treatment Log 36-37

V.

THE DEVELOPMENT OF AN ELASTIC REVERSE GRADIENT GARMENT

TO BE USED AS A COUNTERMEASURE

FOR CARDIOVASCULAR DECONDITIONING

by James F. Annis and Paul Webb

SUMMARY

Using a new Nomex-Lycra elastic fabric and individualized garmentengineering techniques, reverse gradient garments (RGG's) were designed,constructed, and tested for effectiveness as a countermeasure againstcardiovascular deconditioning. By combining torso-compensated positivepressure breathing with a distally diminishing gradient of counterpressuresupplied by the elastic fabric on the limbs, the RGG acts to pool blood in theextremities of recumbent persons much as though they were standing erectin 1 g. It was theorized that through the use of a dynamic pressurizationscheme, the RGG would stress the vasculature in a fashion similar to thatexperienced by the normally active man, hence preventing or limiting thedevelopment of post-weightlessness orthostatic intolerance and relatedconditions.

Four male, college-age subjects received daily treatments with theRGG during a 15-day bedrest study conducted at the NASA Ames ResearchCenter. Four additional subjects also underwent the bedrest, but receivedno treatments; they served as controls. This report describes the designand construction of the garments and gives results of the treatment relatedmeasurements. The results of exercise tolerance tests and studies withlower body negative pressure, of body composition studies, and the resultsof a great number of blood and urine biochemistry tests are to be reportedelsewhere by other investigators; however, the preliminary indication wasthat the RGG was somewhat effective in limiting the deconditioning process.

INTRODUCTION

Astronauts upon returning to earth exhibit varying degrees oforthostatic intolerance. Similar reactions occur when a person stands upafter a period of prolonged bed rest or water immersion. Whether the hypo-gravic weightlessness of space is different in its physiological effects is notclear; however, it is clear that the vigorous exercise regimes of Apolloastronauts and Russian cosmonauts have not solved the problem. Physiolo-gists have generally referred to the complex of conditions noted in connectionwith this phenomenon as cardiovascular deconditioning.

Although the degree of deconditioning that occurs in the individualastronaut is highly variable, it appears that its severity may be directlyrelated to the amount of time spent in the weightless condition. The currentSkylab missions may show that in-flight treatment to prevent or limit cardio-vascular deconditioning should be developed for use in long duration missions.One such treatment approach is described here; it is called a reverse gradientgarment (RGG).

The RGG is an elastic leotard that applies counterpressure to the bodyin such a fashion that blood is pooled intentionally in the extremities when arecumbent subject breathes at selected positive pressures. Using the garmentattempts to simulate for the vasculature the effect of standing erect andwalking in the 1 g environment.

If lack of gravity is the principal cause of the complex deconditioningprocess in the body, and the site of origin is the vasculature, the RGG shouldact as a countermeasure to prevent or limit the development of the condition.To test this hypothesis, RGG's were constructed for four test subjects, whosubsequently received daily treatments with the garment while undergoing a15-day bedrest period to simulate weightlessness. The study was conductedin the Human Research Facility at the NASA Ames Research Center, MoffettField, California. Four additional subjects who underwent the same bedrestperiod but received no treatments with the RGG served as controls. Thisreport describes the background, the principle, and the design and construc-tion of the garments used in the study. Some results from treatment relatedmeasurements are given. The results of the physiological tests conducted byother investigators are to be reported elsewhere, but we have listed the testsperformed in Appendix E.

2.

PHYSIOLOGICAL ASPECTS OF CARDIOVASCULAR DECONDITIONING

The literature dealing with cardiovascular deconditioning is quite lengthybut often not very helpful in explaining how the condition comes about. An ex-cellent accumulation of current knowledge is to be found in "Hypogravic andHypodynamic Environments" (1). Vinograd and Manganelli (2) have prepareda useful summary of the literature dealing with weightlessness counter-measures.

When one simulates weightlessness by bed rest and/or water immersion,a complex of compensatory physiological reactions occurs, reactions thatappear to be similar to those occuring in space flight. McCally and Wunder(3) described a more or less progressive physiological sequence thought tooccur in the hypogravic condition, as follows:

1. The hydrostatic pressure in the vessels disappears;2. there is no peripheral pooling of blood in the capacitance vessels;3. the circulating blood volume is redistributed centrally, and the

intrathoracic vasculature is filled;4. filling results in stimulation of cardiac atrial stretch or

volume receptors;5. antidiuretic hormone (ADH) and aldosterone secretion levels

are reduced via the autonomic nervous system;6. a hyposthenuric diuresis follows;7. this results in a reduction in total extracellular fluid and

blood volume.

The loss of fluid volume may by itself account for the syncopicorthostasis, tachycardia, and narrowing of pulse pressure observed in tilttable tests and lower body negative pressure (LBNP) following weightlesssimulation, as well as for the orthostatic intolerance of returning astronauts.But most investigators feel there is more involved here than simple lossof fluid.

Additional clinical features associated with the deconditioning processhave been reported by Lamb (4) as follows:

1. decreased muscle mass and tone2. decreased red blood cell mass3. reduced bone marrow activity4. reduced coronary blood flow5. increased storage of catecholamine products in the myocardium6. increased nitrogen excretion7. increased calcium mobilization and excretion

3.

Weight loss of 2 to 5%0 of body weight in astronauts appears to benormal (5), even though the relationship between orthostatic intolerance andweight loss is not consistent. In addition, various workers have proposedthat a loss in venous tone or reactivity results in "flabby veins," which aremore compliant and passively fill (when gravity acts on the longitudinal axis),thus effectively reducing the already lowered circulating blood volume. It ispresently too soon to say whether or not an adaptive mechanism developedduring longer stays in space such as Skylab will lessen the physiologicalimpact of return to gravity.

DECONDITIONING COUNTERMEASURES

Regardless of the mechanism of cardiovascular deconditioning, it isclearly a real phenomenon. A number of preventive and corrective counter-measures have been proposed and tested in the laboratory, with varyingdegrees of success. These techniques have included:

1. Venous occlusive cuffs on the extremities (6, 7).2. Elastic counterpressure garments or leotards, worn on

return to the upright position in 1 g (8, 9).3. Periodic centrifugation (10).4. Positive pressure breathing (11).5. Lower body negative pressure.6. Hypoxia.7. Exercise.8. Z-axis trampoline.9. Pharmacologic treatment with salt and fluid retaining hormones.10. Cardiovascular conditioning suit(CVCS)--one variety of reverse

gradient garment.(12).

HISTORY AND BACKGROUND

The development of an RGG required prior knowledge in closely relatedareas of suit technology and physiological evaluation. Webb Associates hadhad experience in constructing garments from powerful elastic fabrics, in theapplication of measured amounts of counterpressure to the body, in the use ofpositive pressure breathing, and in the simulation of weightlessness. Mostclosely related to the present project was a contract we held with the NASALangley Research Center, in 1966, under which we had fabricated and testeda prototype cardiovascular conditioning suit; full details of this work aregiven in NASA CR-1206 (12).

4.

The purpose of the CVCS was to set up a transmural pressure gradientin the circulatory system, while a subject was weightless, similar to thatwhich exists in the erect posture at 1 g. The objective was to determinewhether this pressure gradient would have a beneficial effect in preventingdeconditioning of the vascular system during a prolonged period of simulatedweightlessness. The suit consisted of a series of toroidal bladders enclosingcontiguous sections of each limb and the torso. The bladders were filled withwater and connected to individual-water reservoirs whose height above theimmersion tank determined the internal pressures. The helmet was pressur-ized to 100 mm Hg, as was the topmost bladder on the trunk. From there downto the end of the extremities, the bladder pressures decreased until the handsand feet had no pressure on them at all.. The experimental condition extendedthrough two different 2-week periods, with the subject always horizontal.The first two weeks were a control period, in which the subject lay in bed for12 hours and was submerged in water for the other 12 hours each day, wear-ing no anti-deconditioning garment. During the two-weeks of the CVCS exper-iment, he again alternated -12 hours of bed rest with 12 hours submersion,but this time he wore the CVCS during the time he was submerged, and pres-surization was applied during part of this period. The result was a remark-able difference in the subject's responses following the 2-week control periodand those following the period when he wore the CVCS. His response to 700tilt after the control period was an alarming hypotension and bradycardiaabout the 11th minute, which caused termination of the test. After two weeksof using the CVCS, his response to tilt was normal for him and not at allalarming. The control exposure caused a reduction in his work capacity andhe had a high pulse response to exercise; after the CVCS exposure, thesefactors were normal.

Webb Associates made a second proposal to NASA suggesting thefeasibility of the elastic leotard approach to prevent cardiovascular decondi-tioning, but at that time.the prospects for success of the basic approach werestill uncertain. Since the bladder version of the CVCS produced a positiveresult, interest in the RGG as a possible countermeasure remained.

Meanwhile, in 1967, Webb Associates , again under contract with NASALangley Research Center, made a preliminary study of the feasibility of usingelastic fabric garments for another purpose--for protection against exposureto a vacuum. We constructed elastic sleeves and gloves for two subjects,whose arms were then exposed to near vacuum conditions while wearing theseprotective garments, without incident. The details of this work can be foundin NASA CR-973 (13). Our ultimate objective was to build a complete suitof carefully tailored elastic fabric for wear by astronauts during EVA. Wear-ing such a suit, we thought, would greatly improve the astronaut's range ofmobility and lessen the energy cost of their activities, which had been highwhile wearing conventional gas-filled pressure suits. Hence the new garmentwas given its name--the Space Activity Suit (SAS). In late 1967 we built the

5.

first full suit prototype as a company project; then, from 1968 through 1970a series of prototype SAS garments and a compatible life support systemwere fabricated under contract with NASA Langley Rpe.rch rn+er. Althoug1+.the SAS garments were not designed to apply counterpressure in a gradientfashion, we gained valuable experience in methods of garment engineeringwhich was useful in construction of the RGG's. (14).

PRINCIPLE OF OPERATION

The following basic principles help to explain how the RGG functioned.In the quietly erect man of average. height, the hydrostatic pressure.(PH).in the feet -equals approximately. 100 mm Hg. The value- can be calculated byusing the following relationship:

PH =(rho) gh

where: (rho) = density of the bloodg = acceleration due to gravity

h = height of the column of blood

The transmural pressure (PVT) at any point in the vasculature equalsthe sum of the blood pressure (PB) and the hydrostatic pressure (PH)minus tissue pressure (PC) or intrathoracic pressure (PI):

PVT = PB + PH - (PC) or (PI)

Tissue pressure will be considered to be constant and negligible for the pur-pose of this discussion.

Taking a mean PB of 100 mm Hg, a PH of 100 mm Hg at the feet, and apressure drop of 90 mm Hg across the precapillary arterioles and capillaries,plus another 8 mm Hg across the venous. circulation, the following values forPVT are obtained for the quietly standing- man:

Arterial:, heart level--PVT = 100 + 0 = 100 mm Hg" foot level--PVT = 100 + 100 = 200 mm Hg

Venous: foot level--PVT = 10 + 100 = 110heart level--PVT = 2 + 0 = 2

When a subject is wearing the RGG, the formula for calculation of thetransmural pressure takes the following form:

PVTRGG = PB + PPB - (RGG counterpressure + tissue pressure)

6.

Positive pressure breathing (PPB) is known to increase the blood press-

ure by an amount approximately equal to the increase in breathing pressure

above ambient (15). The increased breathing pressure in the RGG helmet

was counterbalanced by the external forces applied by a combination of the

garment and breathing bladder. This allowed the subjects to breathe at

pressures higher than normally tolerable for long periods of time without

loss of fluid into tissues, discomfort, or syncope. The amount of poolingforced by the PPB-RGG combination should have been essentially equal to

that experienced while standing and moving, since the applied garment pres-

sure to the torso always varied with the breathing pressure and the limb

counterpressures were fixed but decreased in gradient fashion to zero at the

distal ends. For example, using the same values as above for mean blood

pressure and circulatory system pressure drops, the transmural pressures

which develop at heart and foot level when breathing air at 100 mm Hg areas follows:

Arterial: -heart level-.-PT = 100 + 100 - (100) = 100 mm Hgfoot level--PT = 100+ 100 - (0) = 200 mm Hg

Venous: fo6t level--PT = 10-+- 100 - (0) = llOinrniHgheart level--PT = 2 + 100 - (100) = 2 mm Hg

Thus the RGG can recreate the normal erect transmural pressures.The investigator can explore a variety of levels of.pressure treatment without

endangering the subject. Because standing quietly erect at 1 g- for longer

than a few minutes at one time is not normal and may result in over-poolingwith syncope ("parade ground faint"), the constant application of the 100 mm

Hg gradient with the RGG for up to four hours did not seem feasible. Man is

dynamic. He stands, sits, lies, walks, or is otherwise occupied for com-

paratively brief periods of time throughout the day. Any movement bringsthe so-called "muscle pump," i. e. venous pump action, into play and serves

to reduce the hydrostatic effects, especially in the leg veins. Since this is

true, a varying breathing pressure program was adopted for use -with the

RGG. The actual pressure schedule used and the rationale for its use are

discussed in the "Breathing System and Pressure Schedule" section of this

report; see also Appendix A. Since the elastic fabric limb portions of the

garment were engineered to supply a particular gradient, i. e. as though theheart to floor hydrostatic pressure was 50 mm Hg rather than 100, and thebreathing pressure both exceeded and was less than design pressures, the

result was periodic overloading and unloading of the capacitance vessels.

This, it was thought, would more nearly duplicate the normal vascular

stresses required to maintain cardiovascular fitness. Because the subject'shead was enclosed in a full bubble helmet and always pressurized externally

at breathing pressure, the transmural pressures in head and brain were not

affected and were similar to those obtained when lying down even though the

absolute pressure was increased. Syncope did not occur, nor even threaten,during the treatments.

7.

THE RGG SYSTEM

Each of the basic RGG systems consisted of three garment sections,a helmet and bladder assembly, and a Dreating system. A necessary designcriterion was that the garments had to be donned and the system made opera-tional while the subject lay horizontal on a bed. This requirement dictatedmuch of the design adopted. Each of the system components is described inthe sections that follow.

Description of the Garments

Each of the RGG's consisted of three garment sections, which wereworn in two layers. After donning a nylon brief that.was commercially pur-chased, the subject next put on the RGG underlayer, which we often referredto as the slip layer. The lower portion of the slip layer looked much like along-legged girdle.. It.was fabricated completely.of elastic fabric and ex-tended from iliac. crest level to below the knee. - Its construction details areshown in Figure 1; and a photograph of a subject -wearing it is presented asFigure 2. The garment was designed to supply 15-18 mm Hg counterpressure

b - ZIPPER PAD

CROTCH PAD

BLADDER POUCH

POSITIONING PULL

-PAss-THROUGH

HOLDING TAPE

LOCATOR MAR'

ZIPPER

Figure 1. Line drawing of the slip layer girdleshowing some construction detail.

8.

Figure 2. Photograph of subject wearing slip layer girdle.(Picture taken during bedrest treatments.)

on the thigh at crotch level. The counterpressure was held constant abovethat level and reduced proportionally at 5 cm linear distances below thecrotch level so that end counterpressure at the bottom was 1.5 mm Hg. Theincremental decrease in counterpressure gradient was somewhat variablefrom subject to subject and was dependent upon the total leg length covered.Donning was accomplished via two full length lateral, jacket type zippers(open top and bottom), which were closed once the subject was rolled onto thepre-positioned garment. (All zippers were supplied by the Talon Division ofTextron, Inc., Meadville, Pa.) Special features of the girdle undergarmentwere:

1. zipper pads: composed of 5 mm-thick foam urethaneencased in a white, lightweight, nylon-spandex fabric.

2. crotch pad: bilateral and overlapping countoured,elipse-shaped pads measuring approximately 25 cmx 10 cm wide. Same components as above.

3. bladder pouch: envelope to contain expansion bladderand/or counterpressure measuring devices (inside),with appropriately located pass-through holds for airlines and wires. Constructed of RGG fabric.

9.

_ _ _ _ _

4. Holding tape: nylon bias tape sewn to medial midlineseams for the prevention of vertical displacement ofcounterpressure gradients.

5. Positioning marks: subject's special anatomicallocations, e. g. knee, crotch level, etc., denotedby red marks; also medial holding tape marked inred at each 5 cm increment.

6. pull tabs: loops of Nomex non-stretch fabric (Dupont)sewn to medial holding tape to assist in propergarment positioning.

7. seams: all main seams were sewn with nylon thread(Premier Thread Co., Bristol, R. I., type VT295)using stitch type 605 (5 threads).

Figure 3 (line drawing) and Figure 4 (photograph) show the upper por-tion of the undergarment. This piece covered the entire torso and the armsto just below the elbow. The torso portion of the garment was not engineeredto supply a gradient of counterpressure but to supply approximately 5 mm Hgof pressure throughout. Since the garment lay under the breathing bladder,we wanted it to be form-fitting but not tight. Subsequent to fitting trials,additional fabric was added over the rib cage to lessen the work of breathingagainst the elastic fabric.

ELASTIC CORE

- AXILIARY PAD

ZIPPER

ZIPPER (REAR) POSITIONING

PULL TBE

PAD - -- ELASTIC CORE

HOLDING TAPE I

VELCR.

CROTCH STRAP

Figure 3. Line drawing of the slip layer top.

10.

Figure 4. Photograph of subject wearing complete slip layer.(Picture taken during the treatments.)

Sleeves were attached along the scye line and extended approximately10 cm below the elbow. The counterpressure gradient ranged from 25 mm Hgapplied at the axillary fold level linearly down to 10 mm Hg at the distal end.The actual distal end pressure, hence the gradient, varied somewhat fromindividual to individual; however, the overlayer pressure gradient was ad-justed so that the net total pressure gradient supplied to the arms was thesame for all subjects. The bottom of the torso part of the garment overlappedthe interiliac area of the pelvis covered by the girdle section. This part wasanchored via a strap which was passed through the crotch (front to back) andheld in place by strips of Velcro (Velcro Corp., New York, N. Y.). Entry intothe garment was via a full-length rear midline zipper (open top and bottom)and zippers which extended from the neck opening over the mid-shoulder lineto the end of each sleeve. Donning was performed by positioning the garmenton the supine subject (zippers open), closing the arm zippers, then rolling thesubject 900, closing the rear zipper, and attaching the crotch strap.

Special pieces in which the elastomic core ran vertically up and overthe shoulder were inserted to improve fit and supply counterpressure to the,area. Vertical length measurements from the torso were reduced 5% in thetorso section of the garment to increase shoulder counterpressure and gen-erally improve fit. In addition to axillary pads, there were pads positionedover the antecubital area to limit fabric pinching and cutting associated witharm flexion.

11.

Immediately over the undergarment layer and next to be donned wasthe breathing bladder assembly, including the neck seal, lower helmet sealring, and the split breastplate assembly. These will be more fully describedin the next section.

The outer layer consisted of a full body garment, the function of whichwas to complete the limb counterpressure gradients and to provide restraintfor the torso pressurizing bladder which lay under it and also to act as ahold-down for the helmet during the pressure breathing.

Limb counterpressure gradients were designed to complement theunderlying garment so that the desired total limb pressures were obtained.For example, on the legs the slip layer was designed with a 15-18 mm Hg(crotch level) to 1.5 mm Hg (just below the knee) gradient. Since we wanteda total counterpressure on the uppermost thigh which would give an effective50-60 mm Hg total right heart level gradient equivalent at that level, the outergarment had to make up the required difference. It was known from previouswork that counterpressure totals of garment layers are not simply additive,but rather approximately 0.80 times the total. Therefore this factor wastaken into account in engineering the outer layer. If, for example, a totalof 40 mm Hg combined counterpressure was needed at the crotch level for agiven subject, the design counterpressure had to be 1.25 times that value.Also, since the underlayer ended just below the knee and gradient calcula-tions were based upon total heart to floor distance, the outer layer gradientwas not simply linear because it assumed the full counterpressure burdenbelow the knee. Similarly, on the arms the outer layer assumed the totalcounterpressure requirement below the end of the slip layer so that the com-bined gradient was a linear continuum of reducing counterpressure towardthe wrist. The pressurization scheme of the complete assembly is given inthe section of this report entitled Fabric Engineering (see Figure 15, page 32).

The same basic pattern scheme that was used in the construction ofthe two-piece underlayer was again used and re-engineered to fabricate thefull garment. A sketch and photograph provided in Figures 5 and 6 show thedetail and appearance of this garment.

A.s can be seen in the figures, this garment was equipped with twofull-length leg-torso zippers and also arm zippers. Donning was accomplishedby rolling the subject from his side onto the unzippered garment, which hadbeen pre-positioned to be properly located when he was again on his back.The front flap created by the two torso zippers (when unzipped), which waslaid between the leg sections as part of the pre-positioning process, was thenplaced over the subject's torso and the long zippers closed. Next the arm-shoulder zippers were closed. Finally the secondary zippers were closedover the thigh area. These zippers were added to furnish limited accessports and to make closure easier in a high counterpressure area.

12.

HELMEi HOLD-DOW" TRAP

50 MMHG

Z IPPER Figure 5. Line drawing ofNONSTRETCH NOMEX the outer full-body garment

TORSO LACE TAPES showing some design

ELASTIC FABRIC (ARM) features.

JUNCTION OF Two FABRICS12.0 MMHG 40 MMHG

FULL LENGTH ZIPPER

LEG LACE TAPES

ELASTIC FABRIC (LEG)

RETAINING STRAP

3.5 mMHG

Figure 6. Photograph of subject wearing full RGG assembly, with helmetbeing positioned. (Picture taken during the treatments.)

13.

C 4

The helmet hold-down straps were then slipped through the bucklestraps which were attached to the breastplate assembly and pulled tight.Finally, to complete the dressing procedure, the helmet was positioned andlocked into place. Throughout the procedure, care was taken to locate thegarment correctly; the subject's locator marks on the garments assisted inthis job. The entire dressing procedure normally took 15 minutes.

Breathing System and Pressurization Schedule

Breathing System.--The breathing system that supplied positive pressure airto the subjects was a variably-back loaded, free flow type. Duplicate systemswere fabricated so that two subjects could be treated simultaneously. Wedeveloped the following design requirements:

1. Must be safe and reliable.

2. Must supply good quality breathing air (e. g. oil free).

3. Flow rate must not be grossly affected by changes in pressure.

4. Must supply at least 75 to 1001pm at all pressures used(0 to 100 mm Hg).

5. Must be capable of programmed and automatic pressure regulation.

6. Must be portable and lightweight.

7. Must be simple to operate.

8. Must be adaptable to rapid change in pressure programs.

The systems ultimately developed met all of the above criteria and performedwell during the treatment program. The components and their arrangementare depicted in the diagram given in Figure 7.

7 92 An n Figure 7. Arrangement1 2of the breathing system

-0 components.

1 INTAKE FI Tr . 10 DIFFERENTIAL PRESSURE TRANSDUCER2 COMPRESSOR II SIGNAL CONDITIONER3 PRESSURE RELIEF 12 RECORDER

4 RALL 13 BREATHING HOSE

5 INSTRUUENT RACK 14 HELME-

6 PRESSURE GAUGE 15 TORSO BLA OR

I MUFFLER 16 PRESSURE REGULATING VALVE

8 BACK LOADING VALVE 17 FLEXIBLE MERCURY COLUMN

9 FILTER 18 PRESSURIZATION PROGRAMMER

14.

Air was supplied to each system by a small carbon vane compressor(Gast Mfg. Co., model no. 0440-P103A), via a pop-off valve, filter, muffler,backloading needle valve, pressure gage, and secondary safety relief to thehelmet. The compressors were pallet mounted and during the treatmentswerelocated in a utility chase adjacent to the treatment room in order toisolate the noise. The remainder of the components were rack mounted andlocated in the treatment room. To smooth pressure fluctuations, the com-pressors were back-loaded to 238 mm Hg (4.5 psi). The first relief valve wasset to approximately 360 mm Hg (7 psi), and the secondary relief consisted ofa brass plug resting on an orifice. The weight of the plug was calculated tolift off whenever the pressure in the helmet exceeded 100 mm Hg. The airflow rate averaged nearly 100 1pm at breathing pressures of 25-50 mm Hg andwas reduced to 80 ipm at breathing pressures of 100 mm Hg. Measurementsof flow were made on-line during the treatments using a small turbine flow-meter (Wright spirometer, British Oxygen Co., Ltd., London, England). It wasestimated that the functional volume of the helmet-bladder complex wasapproximately 15 liters; therefore, with a washout rate of 5 to 9 times perminute, C02 buildup was not a problem. Breathing pressure in each systemwas sensed by a differential pressure transducer (Schaevitz Engineering Co.,Camden, N. J., model PTA-310D-100W). A signal conditioner serviced bothtransducers and the pressure of each system was monitored by a meter andcontinuously recorded on a strip chart recorder.

The interconnecting lines to and from the helmets were oxygenbreathing hoses reinforced with wire and covered with cloth. They measured1.9 cm (0.75 in.) ID. (R. E. Darling Co., Gaithersburg, Md., REDAR A10986-1).The length of hose (in and out) was 3 meters for the first few days of treat-ment. Later an additional 3 meters of hose was included in the in-comingline so that it could be coiled in an ice water bath to cool the breathing air.

Helmet effluent was routed to a back loading type of regulator,which established the system pressure. The loading of the valve was accom-plished by varying the height of a mercury column. The height of the mer-cury loading column (hence the system pressure) was varied automaticallyby an aluminum cam or pressure programmer which raiser or lowered thecolumn as it turned. The cam was driven by a synchronous motor geared toproduce one complete revolution of the pressure profile cam each 30 minutes.In operation the cam varied the breathing pressure over a range of pressurefrom 25 mm Hg to 100 mm Hg. A portion of the cam contained a movableflange which allowed a low pressure (less than 15 mm Hg) starting point.After starting, the flange was locked into the operating position. The shapeof the cam was dictated by the selected pressure profile. The size and shapeof the cams for the two systems were identical. A simplified sketch of thepressure regulating components of the breathing system is given in Figure 8.

15.

Clamp Bearings

Loading Diaphragm C

Mercury Column Drive Motor

Air AdjustingOut - Flange

Support

Air In

PRESSURE REGULATING VALVE PRESSURIZATION PROGRAMMER

Figure 8. Sketch of the pressure regulating componentsof the breathing system.

The type of pressure control system used allowed considerable selec-tivity in treatment pressure programs. For example, if considered necessary,a single constant pressure level between 15 and 100 mm Hg could be obtainedby simply turning off the cam drive motor at that point. Also the level of theselected pressure profile could be increased on decreased by changing therelative position of the back loading valve to the cam. Because of possibledifferences in operational pressures and flow rates in the two systems, andto minimize any possible effects therefrom, the subject-breathing systemcombination was switched each treatment day.

Pressurization schedule. -- There were two sets of pressures involved in theRGG: the breathing pressures and the mechanical counterpressure of theelastic suit. The suit pressures applied to the arms and legs were fixed inthe suit design and tailoring. Once the suit was donned, these pressures didnot change, but the torso pressure did vary with the air pressure in thehelmet and bladder.

Helmet and bladder pressures, which were equal, varied dynamicallyduring the treatment period. The reason for varying pressure was that aproperly chosen schedule of pressure more closely simulated the stress ofnormal living on the vascular system.

The stress we were interested in simulating was the hydrostatic load-ing of vessels below heart level whenever a person is upright. Since normalliving involves varying periods of standing, sitting, walking about, and lean-ing against the wall, so the hydrostatic loading varies considerably throughouta normal day. 100 mm Hg is the hydrostatic loading pressure usually givenfor an erect man in a 1 g environment, so a pressure schedule of four hours

16.

at 100 mm Hg would be a simulation of a relaxed man standing upright--leaning against the wall, perhaps. When the man tenses his leg muscles orwalks around, venous pressure in the foot decreases to somewhere between

10 and 30 mm Hg. When he sits, relaxed, the loading of leg and feet veinsdecreases to about 50 mm Hg. These considerations led to the dynamic.pressure schedule depicted in Figure 9. The first portion of each 30-minutecycle was spent with a pressure in the helmet and bladder of 50 mm Hg, whichwas proper with the designed gradient applied by the elastic suit at the proxi-mal ends of the arms and legs. The other portion of the 30-minute cycle wasoccupied with sinusoidal pressure swings between 25 and 100mm Hg.

100

90

80

70

50

L 40 'I-

- -Z.e L E V EL E N D

5 10 15 20 25 30

TIME - MINS.

Figure 9. Curve showing the profile of the pressure scheduleused during the RGG treatments.

We chose to precede the excursion to 100 mm Hg pressure with a dipto the minimum pressure of 25 mm Hg in order to permit the greatest venousreturn to the thorax (the greatest "unloading") which the suit would permit.This was then followed by the high pressure which caused the least venousreturn to the thorax--hence the greatest loading, or stress on the circulation.Finally, breathing pressure decayed through the low point again, then to50 mm Hg, and finally to 25 mmHg to start a new cycle. A sinusoidal form waschosen as opposed to a ramp or step function change because the sinusoid waseasier on the ear drums. Subjects quickly learned how to create neck sealleaks, hence lowering the pressure, especially during the 100 mm Hg peak.In so doing they occasionally experienced more rapid changes in pressures.Changes from 100 mm Hg down to 25 in as little as one second were observed.Most subjects experienced no difficulty with this maneuver. Although thisform of voluntary pressure change disrupted the fixed schedule, it was nottotally discouraged by the observers since it was in agreement with the goals

17.

of the selected schedule and considered good therapy. A more completereview of the rationale for the selected pressurization schedule is providedin Appendix A.

Helmet and Bladder Assembly

Two full bubble helmets were used. The helmets consisted of a poly-carbonate plastic bubble, interconnecting rings and seals, and a hinged base-plate clamp with a molded fiberglas breastplate. A torso pressurizing-breathing bladder was attached to the neck seal ring assembly. A photographof one of the helmets is provided in Figure 10.

Figure 10. Photograph of one of the full bubble helmetsused during the RGG treatments.

18.

The two helmets had been used previously in our development of the

Space Activity Suit (13, 14) and required some minor changes, as follows:the head-set shown in the photograph was replaced by a pillow speaker whichwas located on the anterior crown area of the bubble. A new microphone(Pacific Plantronics, Inc., Santa Cruz, Calif., type MS50/T55-16) and throughconnector were installed. The breathing air ports were replaced by aluminumfittings which opened laterally rather than dorsally. This modification wasnecessary to facilitate connection of the air hoses on the recumbent subjects.All seals were replaced by new material. The neck seal and reflected dam(comfort pillow) were constructed of 0.32 cm (0. 125 in.) thick nyloprene.Cemented joints were hand sewn with nylon thread for safety. The helmetswere leak and pressure tested to 500 mmHg (10 psi) before use. Thearrangement of the helmet and torso pressurizing-breathing bladder is shownin Figure 11.

Helmetbubble

Figure 11. Cross-sectionalview showing the arrangement

. of the helmet, comfort pillow,and torso bladder.

helnet-bladder r drinterconnecting t ill )airway

breastplate

toraopressurizingbreathingbladder

As can be seen, the airway was continuous with the bubble and thecomfort pillow. The comfort pillow was so named because upon helmetpressurization the pillow inflated to cushion the fiberglas breastplate whilepressurizing the shoulders. The entire assembly was restrained by four2.5 cm (1 in.) wide nylon web belting straps equipped with buckles. The strapswere anchored to the breastplate assembly and the outer RGG garment. Uponpressurization the force was distributed through the non-stretch Nomex fabric

19.

of the torso section of the garment so that crotch pull even at the higherpressures used in treatments (100 mm Hg) was quite tolerable.

The torso pressurizing-breathing bladder was constructed of rubber-ized neoprene-nylon twill fabric (Richardson-Chemprene, Inc., Beacon, N. Y.,#21433). Since the bladder was contiguous via a large opening (5 cm diameter)with the helmet air supply, the pressure in the bladder was always the sameas that in the helmet. The bladder served not only to counterbalance the torsowith the breathing pressure but also as a volume compensating plenum tofacilitate breathing. The bladder coverage and design are shown in Figure 12,below, and also in Figure 15, page 32.

Air Flow

Supplementary Helmet Lower SealSupplementary Ring

Bladder(s) Ring

Torsoi I Bladder

SupplementaryBladder (s)

Figure 12. Sketch showing the position and coverageof the torso pressurizing-breathing bladder

and the supplementary bladders.

Dimensions for sizing the bladders were taken from subject measure-ments. Since there were only two bladders for the four subjects, one wassized to fit the two large subjects and the other to fit the smaller two. Duringprototype evaluation tests, it was learned that additional coverage not designedinto the original bladder was desirable. Subsequently four small supplemen-tary bladders were added, two on the front of the shoulder and two in the groin.The bladders were not connected to the breathing air supply but were inflatedeither orally or with a blood pressure cuff bulb to the desired pressure. Thebilateral anterior shoulder bladders acted to prevent the development ofpetechiae in the subclavicular area during the treatments. The groin bladderswere used to increase comfort in an area where main bladder pressure endedand where the elastic pressure of the garment could not be well applied.

20.

Expansion of the main torso bladder was controlled by adjustment of the torsolace tapes on the garment. The volume of the main bladder during operationwas maintained at approximately ten liters.

GARMENT DESIGN AND CONSTRUCTION METHODS

One of the early tasks in the RGG project was writing specificationsand placing a subcontract for the development of a new fabric, which ultimatelyproved to be very satisfactory. In order to tailor the garments and engineerspecific counterpressures, we had to know not only the physical properties ofthe fabric but also the dimensions of the person to be fitted; therefore thetest subjects were selected as early in the project as possible. The four sub-jects selected to wear the RGG were measured in great detail. Meanwhile,during fabric production and subject selection and measurement, designstudies had resulted in a preliminary pattern layout for garment construction.The subject measurements were then prepared for sizing the individualpattern pieces of each garment. Using a laboratory technician as subject(who had also been measured), a series of prototype garments was fabricated.The information gained from design, fit, donning, and counterpressuremeasurements on these garments was used in the fabrication of the final testgarments. Meanwhile, related instruments and hardware to complete theRGG system were being purchased or fabricated. A series of complete sys-tem test runs was made in our laboratory, using the technician as subject,wearing his prototype test garments. As a result of these tests, a number ofcorrections and modifications were incorporated into the final test assem-blies. The total production time from subject selection to the start of thebedrest study at Ames Research Center was 4-1/2 months.

The above paragraph outlines the RGG production tasks as they wereperformed in the project. In the following sections, each of the variousaspects of the.design and production of the RGG's will be dealt with.

Fabrics

Early in the project specifications were issued for a new fabric to bedeveloped for constructing the RGG's. We felt that a new fabric was requiredfor the following reasons:

1. Past experience with available elastic fabrics had shownthat they all had one or more undesirable characteristics,such as poor retention of original physical properties,poor sewability, poor hand (feeling to touch), tendency toravel, limited porosity, limited elongation, or low power.

21.

2. A comprehensive physical description and test of the fabric,

usually not available with "off-the-shelf" fabrics, were needed.

3. We could make a start toward a space-qualified fabric

by incorporating properties such as low flammability.

The specifications were sent to three possible suppliers, and the subcontract

was ultimately awarded to a firm specializing in fabric development,

Prodesco, Inc., of Perkasie, Pennsylvania.

Many types of elastic fabrics are available today, both woven and

knitted, made of fibers including many kinds of rubber filaments and various

synthetics. One synthetic that has found wide commercial use is spandex,

a species within the polyurethane elastomer group. In elastic fabrics, the

elastic fibers usually run parallel through the length of the fabric matrix

(warp or wale) and are held in position by cross fibers (weft, courses) of a

non-elastic yarn (see Appendix B). Spandex elastomers have particularly

good specifications with regard to elongation, set, shelf life, and inertness.

The four major types of elastic fabric are bobbinet, powernet, tricot, and

circular knit. We have had most experience in working with bobbinet and

powernet, since these were used to construct the Space Activity Suit garments.

Using powernet fabrication procedures, our subcontractor, Prodesco,

produced 14 variants, from which one fabric constructed of spun Nomex

and Lycra (both DuPont) spandex yarns was selected as possessing properties

nearest to those specified. A limited production run was made, but the

finished fabric was not usable because of a high number of defects. Since the

problem appeared to be related to the Nomex yarn used, a second run was

made using a different Nomex yarn that had been used successfully before.

The resulting fabric (sage green in color) had physical properties very

similar to the first but its defects were minimal. It was this fabric from

which the elastic segments of the RGG were constructed. A complete descrip-

tion of the fabric including the test data, as prepared by the fabricator, is

presented in Appendix B.

As decribed earlier, the torso section of the full body garment was

constructed of a non-stretch fabric, which served two purposes. It acted to

retain and shape the inflated bladder, and it served as the helmet restraintbase to prevent or limit the helmet rise associated with pressurization. Atthe highest breathing pressure, the fabric had to restrain a vertical force of

approximately 70 lbs. The pull was transferred largely to the elastic thighportion of the garment, and crotch pull even at 100 mm Hg helmet pressurewas quite tolerable. The non-stretch fabric was 100% Nomex, sage green,and was originally developed for construction of U. S. Air Force anti-G suits.A listing of the physical properties of this fabric is given in Appendix C.

22.

Subjects and Measurements

Selection. -- From the group of subject candidates interviewed, eight wereselected to participate in the study, four to be suited with the RGG and fouras controls. All subjects were male college students. Placement in thetreated or control groups was based upon individual willingness to wear thegarment, group pairing based upon height-weight relationships, and the re-sult of preliminary orthostatic tolerance and fitness tests performed in theWebb Associates laboratory. The objective was to balance as closely aspossible the physical and physiological characteristics of the two groups.Prior to final selection, subjects were fully instructed about all aspects ofthe testing protocol and voluntarily signed the human research informedconsent forms. Also, complete medical exams had to be passed. As a resultof the medical exams, one of the original eight subjects was dropped andlater replaced by control subject GL (#5). Two groups, each composed oftwo treated and two control subjects, were formed, and each subject wasassigned a test number. Basic anthropometric data for all eight are pre-sented in Table 1, below.

Table 1.Basic Physical Characteristics of the Subjects

Subject # Age' Stature Weight& initials yrs cm percentile** kg percentile *

Group suited 1 FF 21 177.1 49 85.5 7611 4 DS 22 184.3 87 69.5 17I

control 2 TC 21 176.5 45 84.1 72" 3 RR 20 179.1 62 70.5 21

Group suited 7 TH 20 170.5 14 60.7 2" 8 AH 19 181.6 76 73.2 30

control 5 GL 26 174.0 30 75.5 38" 6 MS 20 179.1 62 72.7 28

At time of selection.

Percentiles based upon values from Anthropometry of U. S. Air ForceFlyers--19 6 7 Survey. (Unpublished data, Anthropology Branch, AerospaceMedical Research Laboratory, Wright-Patterson Air Force Base, Ohio.)

Measurements.--Since the RGG had to be carefully fitted as well as engin-eered for proper counterpressure gradient application, the subjects for whomsuits were constructed had to be thoroughly measured anthropometrically.A total of 320 discrete measurements was taken on each of the four subjectswho were to be fitted with RGG's. Approximately 100 of the measurements

23.

can be considered classical anthropometric descriptors, and the remainder

were needed for tailoring and engineering purposes. All measurements were

performed manually by experienced anthropometrists using standard anthro-

pometers. All measurements were recorded to the nearest millimeter on

prepared forms. So that the suited subjects can be physically characterized,

a group of selected measurements is given in Table 2. Procedures used for

the more standard measurements, as well as selection of landmarks, were

based upon techniques used in recent anthropometric surveys (16). All

measurements were taken with the subject standing, after some discussion

about the measurement of leg circumferences. Should they be taken with the

subject lying down, since the garments were to be worn in bed? We decided

not to do this, since the dimensional increase that occurs relative to hydro-

static blood pooling in the erect person's limbs should be included in suit

pressure gradient calculations.

A preponderance of circumferential or girth measurements was

needed for garment pressure engineering. The reason for this is explained

in the next section of this report (Fabric Engineering). Since the procedures

used for obtaining these and other special tailoring measurements are not

standard, a brief outline of the methods used is given below:

1. Lateral midlines for the legs and torso from the floorto the axilla were defined and marked on the skin,

using a colored, fine felt-tip pen.

2. Starting at the tip of the lateral malleolus (zero level),ink marks were made on the lateral midlines at 5 cm

increments. A. flexible steel measuring tape, made to

conform to body contours and divided into millimeters,was used.

3. Special anatomic landmarks, e. g. calf maximum girth

level, patella, crotch, iliac crest, nipple level anterior,axillary fold level, etc., were located and marked on the

lateral midline wherever they fell.

4. With the arms in the anatomic position (thumbs out), thelateral midline-5 cm increment grid was drawn on theskin of the arms.

5. Special features of the arm, e. g. forearm maximumgirth level, elbow, mid biceps, etc., were denotedon the line.

6. On the torso from crotch to suprasternale (front), andcoccyx to cervicale (rear), the medial midlines weredrawn. The zero level mark for the lines was referencedto the nearest 5 cm mark on the lateral midline.

24.

7. All anatomic landmark levels of the torso were alsomarked on the medial midline.

8. Each shoulder arch was divided into anterior and posteriorhalves along the mid-shoulder line and then ruled horizon-tally and vertically in a 5 cm grid pattern. This areacovered from the level of the axilla laterally to the extensionof the neck angle line both front and back.

9. With all measurement points located, the leg and torsocircumferences were obtained every 5 cm, progressingfrom the zero reference upward.

10. Above crotch level, all circumferences on the torsowere recorded as portions of the quadrant defined by

the midline marks.

11. The arm-shoulder complex was measured similarly.

Throughout the measurement procedure an effort was made toeliminate errors in transcription of values or errors induced by tapepressure, skin deformation, or subject movement. A number of new andspecial measurements were developed; this was particularly true for thecrotch and shoulder areas, which were known to be difficult to fit.

Fabric Engineering

When subject dimensions and fabric properties are known, it ispossible to produce a selected counterpressure to be provided by the finishedgarment over a specific body site, although this is strictly true only for themore cylindrical portions of the body. The pattern size is dependent uponthe counterpressure to be applied on a given diameter and the amount ofstretch the fabric must undergo in order to supply that counterpressure.The amount of force or tension on the fabric when stretched is a function ofthe elastic modulus of the fabric and must be known. This value is simplythe ratio of the applied extending force or stress, as expressed per unitlength of fabric, to the proportionate change in length from the unloaded value(extensibility ratio). Stress-strain or power curves for an elastic fabric aredetermined on a textile testing machine, and are usually expressed in termsof percent elongation (as compared to the original length of the test piece)at a given force per unit width of material. Power curves at three differentloading levels were determined for the powernet fabric used in RGG con-struction. Curves for the finished fabric in the wale direction have beenreproduced in Figure 13.

25.

Table 2.

Selected Measurements of the Treated Subjects1

Measurement SubjectFF JH AH DS

Weight 2 85.5 kg 60.7 kg 73.2 kg 69.5 kg

Heights:stature 177.1 cm 170.5 cm 181.6 cm 184.3 cm3rd intercostal space--right 3 133.2 129.3 136.6 142.0cervicale 150.2 143.5 153.3 156.3chin 153.5 145.7 156.4 160.7suprasternale 143.4 137.6 147.1 148.1acromiale 4 144.1 138.9 144.9 149.2crotch 85.3 78.7 83.2 .88.6dactylion 4 65.1 69.2 66.3 68.4trochanteric 4 --- 88.3 98.7 97.3patella circumference 4 49.1 45.6 49.6 51.4medial malleolus 4 8.8 8.3 8.9 9.2

Lengths- BreadthsHead length 18.0 19.8 18.5 19.9head breadth 14.2 14.9 13.2 15.0biacromial breadth 43.8 38.4 42.2 39.4acromion-radiale length 4 29.3 19.0 30.5 35.3radiale-styllion length 4 23.5 31.5 26.5 26.9hand length4 21.0 17.5 19.6 19.4hand breadth4 8.7 8.1 8.8 8.5foot length 4 26.4 25.5 27.4 27.4foot breadth4 11.2 9.5 10.2 10.5elbow bony breadth (humerus) 4 7.4 6.3 6.9 7.1knee bony breadth (femur)4 9.0 --- 8.9 ---

Circumferencesvertical trunk circumference 167.5 160.0 166.2 162.6hip (maximum buttocks) 98.7 86.9 98.5 95.5chest (nipple) 105.7 85.2 92.8 83.8ankle 4 23.4 21.7 21.8 23.4calf (maximum) 4 38.6 34.6 35.9 39.0waist (omphialon) 86.5 75.8 78.2 73.0scye4 50.6 38.6 44.5 37.1biceps (relaxed) 4 31.7 27.7 25.5 27.0forearm4 29.6 24.8 24.9 25.6wrist 4 17.7 16.2 15.3 16.6neck 40.3 36.3 37.5 33.6

26.

Table 2.

Selected Measurements of the Treated Subjects

Measurement SubjectFF JH AH DS

Skinfolds 5

subscapular (R) 11.5 mm 8.0 mm 14.0 mm 6.5 mmtriceps (R) 6.5 4.5 5.0 8.0juxtanipple (R) 6.5 2.5 5.0 3.0suprailiac (R) 20.0 8.5 13.0 8.0mal-xiphoid ('R) 10.5 4.5 13.0 5.0calf (R) 8.5 5.0 7.0 8.5

1For methods, refer to: Anthropometric Survey of Turkey, Greece, andItaly, by H. T. E. Hertzberg, E. Churchill, C. S. Dupertuis, R. M. White,and A. Damon. The MacMillan Co., New York, 1963 (16).

At time of measurements.

3 Used as hydrostatic pressure zero point (2 cm right of sternum).

4 Value quoted is average of right-left measurement.

5 Harpenden caliper.

27.

90

70 LOAD * 0.3 Gc/O

60

LOAD 0.9 OEC

50

40

30LOADL 1 A , /C

20

10

0 20 40 60 80 1 120 140 160 180

PERCENT ELONHATION

Figure 13. Stress-strain or power curves at three load levelsfor the elastic fabric used in RGG construction. Curves are

reproduced from the originals supplied by the fabric mariufacturer.

The relationship between the tension (elongation force) and the coun-terpressure follows the LaPlacian principle, which in its simplest form is:

P = T/r

where P = the applied pressure, T = the tensional force, and r = theradius of the part to be fitted. (For a more complete review of the derivationof the above expression, see our earlier report on the development of theSpace Activity Suit (14).) The appearance of a radius term in the hoop ten-sion formula explains why so many circumferential measurements weretaken on the subjects. Since a great number of calculations was required toconstruct the pressure gradients on the limb sections of each garment, wewished to be able to go directly from each discrete subject measurement to"cut-length" of the relaxed fabric on the garment patterns. This was accom-plished by computerization of the power curve data for the fabric in combin-ation with a modified version of the hoop tension formula for a range of cir-cumferences. Using a piece-wise linearization technique, equations werederived for the 0.3 and the 0.9 kg/cm power curves of the fabric (see Appen-dix B and Figure 13, above.) The resultant program used is given in

28.

Appendix D. - The format used permitted reading fabric "cut-lengths"directly from the print-out for circumferences ranging from 10 cm to 100 cmin steps of 0.25 cm for pressures of from 1 to 49mmHg in steps of 1mmHgeach. After each individual's pressure gradient level was determined ateach circumferential measurement point, one-half working scale patternswere drawn on graph paper. Next, a full scale pattern was constructed foreach garment piece. Figure 14 shows a scaled example of the working lay-out for a leg pattern piece. As shown in the figure, all engineering datarelative to a particular pattern piece were maintained on the 1/2 scalegraphic layouts for a working base and reference. All measurement details,including special anatomic features, were carefully marked directly on theelastic fabric as it was cut.

Additional special considerations that were used in the constructionprocess included the following:

1. The hoop tension formula used in the computer programwas modified to include a factor for change in thicknessof the fabric with elongation. This factor was derivedempirically.

2. The general guideline was used which precluded the useof the fabric to supply more counterpressure than wasobtainable at 80% elongation (of "cut-length") over agiven circumference.

3. Adjustments were made in cut-lengths to account forseaming and insertion of non-stretch componentssuch as zippers.

4. Agreement with ± 10% between calculated and measuredcounterpressures at a given point was considerednecessary to prove the validity of the method.

5. To prevent vertical distortion and/or dislocation ofthe garment when donned, holding tapes and non-stretchable zippers were located strategically.

Since the garments were designed and constructed with a fixedpressure gradient on the limbs, we were anxious that some degree ofadjustability be included. If significant weight loss were to occur duringbed rest (which it did not), the garments would need to be re-tensionedin order to maintain the original gradient pressure level. Also, if a treat-ment program or pressure level needed to be altered, the garments shouldbe equipped to handle the change. Both of these objectives were accom-plished by the insertion of lace tapes and bladders in the leg sections of thegarment. No provision for altering arm counterpressure was made.

29.

CIRCUMFERENCE INCREMENTALEASUREMENT

POINTS

a21.2 90 CMP

27.0

FABRIC CUT LENGTH 31.1 = CM COUNTER PRESSURE

31.0 cM 5,82 78 rm CROTCH 22.0 MMHG29.9 5 75 c210

30.8 5 70 20,0

31.2 54 65 cm19,2

60 CM31.3 518.5

30.6 48.3 55 -17.830.6

43.4 50 CM29.4 17.128.4 -9, 45 CM

28.5 38 40 ID-PATELLA -15.6

27.3 5,5 35 cM 14.9

28.4 - 36.8 30 cm 14.2

30.3 3q.7 25 rm _13.5

309.8 22 CM CALF -- 13,430.5 - 39.5 20 CM30.6 - 12.8

29.5 06 15 12,0

26.7 _ 30.2 10 CM 9,8

23, -1 25.4 5 7.6

22,1 _ 0 LAT, MALLEOLUS 5.,4

FLOOR

Figure 14. Reproduction of a working layout leg patternfor an actual RGG full body garment.

30.

The lace tapes, similar to those used in partial pressure suits,were made of white nylon (Sherman Textile Corp., Pawtucket, R. I.,#S/903). They were located over the thigh and calf region of each leg butinterrupted across the knee joint. The loop tapes were spaced so that agiven increment of tightening resulted in a known amount of increased coun-terpressure while retaining the gradient scheme. For example, 2 cm oftake-up in the laces over the length of the tape would increase the pressureby 10 mm Hg. Lace tapes were also sewn to the anterior midline and lateralmidlines of the non-stretch Nomex over the torso area. These served tocontrol the size of the inflated breathing bladder (see Helmet and BladderAssembly).

Provisions were made for the insertion of pressurization bladdersunderneath the lace tapes; they were constructed of the same neoprene-nylon fabric used to make the large torso bladder. These bladders wereremovable and inflated independently of the breathing system. They weredesigned to supply an additional 5 mm Hg of counterpressure along thegradient when fully inflated. Also, it was intended to use these bladdersunder tightened lace tapes to prevent pinching.

The counterpressure supplied to the body by the complete RGGassembly is shown in Figure 15. The pressurization of the torso variedbetween 20 and 100 mm Hg and followed the pattern established by thebreathing pressure schedule (see Breathing System and PressurizationSchedule). The pressure gradients on the limbs were fixed by the elasticfabric engineering and were basically the same for all subjects. As describedabove, the leg counterpressure gradient could be increased through the useof bladders and lace tapes, if required. The only areas of the body where thecounterpressure cannot be accurately stated correspond to the location ofthe supplementary bladders. Since exact engineering of the fabric could notbe performed for these areas, proof of proper pressurization relied uponprevention of localized low pressure effects during operation, e. g. petechiaeand edema. The decision not to include the torso below the heart level inthe gradient of pressure was based upon the suspicion that a gradient ofpressure would not properly transfer to the abdominal vasculature andthat a large amount of blood pooling might occur there. The RGG was de-signed to preferentially stress the limb vasculature, which we consideredto play a large role in the deconditioning process.

31.

HELMET (20-100 mmHg)

AI R -0 ,--0,.FLOW

COMFORT PILLOW

SHOULDER, SUPPLEMENTARY (20-100 mmHg)BLADDER Torso(Intermediate Pressure) - AXILLARY LEVEL5m Bladder

cm(20-100 (50 mmHg)m m H g )

IGradient

- Counterpressure

S3.8 mmHg/5cm

SUPPLEMENTARY BLADDER(Intermediate Pressure) RADIAL STYLOID PROCESS

CROTCH LEVEL (12 mmHg)(40 mmHg)

FINGER TIP (O mmHg)

GradientA Counterpressure

2.3 mmHg/5cm

5cm Measurement Increment

(5 mmHg) -LATERAL MALLEOLUS(0 mmHg) -- FLOOR

Figure 15. Sketch showing the pressurization scheme of the complete RGG system.

32.

ACCESSORY EQUIPMENT AND METHODS

Counterpressure Measurement'Device

The tightness of fit progressing centrally on the limbs, the visiblechange in spacing of the fabric threads and elastic core along the limbs, andthe obvious peripheral venous engorgement in the hands and feet, were allevidence that the RGG's were producing a gradient of pressure. However,these observations said little if anything about the actual level of counter-pressure applied at a particular point under the garment. A method for deter-mining the suit applied pressure at the skin-cloth interface was thereforedeveloped. From our previous experience we had learned that availableminiature pressure transducers were not satisfactory for this purpose. Foraccuracy of measurement at the relatively low pressures to be sensed underthe RGG, the transducer had to be quite large in area but also had to be thin.We had tried pressure sensitive wafers, piezoelectric disks, but with limitedsuccess, since repeatability is poor. For bench testing of counterpressurewe have found the blood pressure cuff bladder and gage to be a satisfactorymethod. However, the standard bladder is large and thicker than preferred.Also the counterpressure is taken to be that pressure which occurs at theinstant the bladder first starts to expand. The detection of this instant re-quires the use of a motion detector of some sort. For this purpose we haveused instruments which measure change in limb girth (see venous compliancetest--Helex). This method was considered unsatisfactory for use during thebedrest testing. In this study we used another variation of the inflated bladdertechnique. The sensor used is similar to a pressure switch in concept. Thedevice is depicted diagrammatically in Figure 16. Once in place under thegarment, air was pumped into the bladder. At that point when bladder pres-sure equaled applied pressure the bladder expanded, the contacts separated,and a battery powered light went off. Bladder pressure was simultaneouslymonitored on an aneroid gage.

Neoprene - Seal

Nylon Fabric

Figure 16. Line drawingshowing internal detail ofthe garment counterpressure Contactssensor. Top bladder coverremoved to show detail. C

Air Line

33.

Bladders were constructed of rubberized nylon fabric and sealed aroundthe edges. The contacts were of 200 mesh stainless steel screen wire, 1.5 mmwide. The inflation tube was 3.175 mm OD x 1.6 mm ID plastic tubing. Twosizes of bladders were fabricated, with an effective inflation area of 12.5 cm 2

and 6 cm 2 . The bladders were approximately 1.5 mm thick, and so did notappreciably distort the skin or the fabric. The bladders were usually positionedin the garment just prior to closing. All transducers were bench calibratedusing a recorder to detect true pressure endpoints. To simplify operationduring the test, the squeeze bulb, signal light, aneroid gage, connecting lines,and battery pack were incorporated into a single instrument cabinet.

Venous Compliance Measurement

Because quantatative data indicating the extent of cardiovascular decon-ditioning occurring during the two weeks of bed rest were desirable, we per-formed a simple test of venous compliance on both RGG and control subjects.The technique used was similar to that reported by Newberry and Bryan (17)and utilized by Blockley and Friedlander in the evaluation of the LangleyCardiovascular Conditioning Suit (12). The basic measurement from whichvenous compliance is computed is the change in arm girth as a function ofocclusion pressure of the arm veins. The procedure consisted of applying aseries of cuff pressures to a carefully supported arm with a standard bloodpressure cuff while changes in forearm girth were sensed by a variable-inductance linear transducer connected as one arm of an impedance bridge(Helex Girth Measurement System, Physiometrics, Inc., Malibu, California).Output of the bridge is directly and linearly proportional to the expandedlength of the gage.

The stepwise measurement procedure used is as follows:

1. Place arm in arm suspension system (relaxed, atapproximately 450 above body horizontal plane).

2. Position blood pressure cuff loosely in the standardclinical location.

3. Position pre-calibrated girth change transducer atapproximately 5 cm distal to antecubital fold.Gently massage forearm around transducer.

4. Inflate cuff slowly to 60 mm Hg (1 min.); maintainfor 3 mins; read expansion meter; record.

5. Reduce cuff pressure to 40 mm Hg--read at 1 min.

6. Reduce cuff pressure to 20 mm Hg--read at 1 min.

7. Reduce cuff pressure to 0mm Hg--read at 1 min.

8. Remove cuff and transducer; free arm from suspension assembly.

34.

The total elapsed test time was seven minutes, not including time forarrangement of the arm suspension and positioning of cuff and transducer.The system was calibrated daily just prior to each testing session. Subjectswere instructed to relax in the suspension rig, and care was exercised toduplicate procedures daily. In an attempt to rule out effects of positioningand pressurization rates, a variety of techniques was explored, using our-selves as subjects. No significant differences were observed with repeatedtests. Environmental temperature change, which is known to affect thismeasurement, was not controlled.

TREATMENT METHODS

Testing of the RGG was performed during the two middle weeks of themonth-long bedrest study; actually, the four suited subjects were treated dailyduring the 15 days of actual bed rest. Two subjects were treated simultan-eously in the morning (usually 08 to 12) and the other two were treated in theafternoon (1300-1700). Generally the Group I subjects (FF, DS) were themorning subjects; however, some shifting of morning and afternoon groups didoccur to prevent interference with other test routines. The treatment log,including the daily treatment time, is given in Table 3. The suiting order,bed, and breathing system were rotated daily for each subject. The dailyswitching of breathing systems was introduced to eliminate effects that mightresult from slight differences existing in pressurization levels.

All RGG treatments occurred within the Human Research Facility atNASA Ames Research Center. A room separate from the subjects' normalbedrest station was used for this purpose. Subjects were delivered onwheeled hospital carts to the treatment room and weighed in the supine posi-tion before suiting began. Every second day the venous compliance test wasperformed on both the treated and the control subjects of a given group. Thetreated subjects were tested prior to dressing.

The dressing procedure, already outlined in the suit description section,at first required nearly 30 minutes, but by the end of the first week the timewas down to approximately 15 minutes, including placement of the electrodesfor the ECG. Treatment was considered to have begun when the helmet was inplace. Usually pressurization of the system followed immediately. Each sub-ject's treatment time was monitored by an electronic stopwatch. As can beseen by examination of Table 3, the treatment time after the 4th day wasmaintained at 210 minutes. This amount of time coincided with the establishedlogistical routines. For safety, at least one monitor was always present inthe room with the subjects.

35.

Table 3.

Daily Treatment Log

Group I

Subject #1 -- FF Subject #4 -- DS

total totalDay & date start treatment breathing start treatment breathingof bedrest time time system # time time system #

(mins) (mins)1: 5/7/73 1300 109 1 1330 109 2

2: 5/8/73 0800 150 2 0830 150 1

3: 5/9/73 0830 160 1 0800 161 2

4: 5/10/73 0800 180 2 0830 180 1

5: 5/11/73 0830 210 1 0800 210 2

6: 5/12/73 0800 210 2 0830 210 1

7: 5/13/73 0830 210 1 0800 210 2

8: 5/14/73 1330 210 2 1300 210 1

9: 5/15/73 0800 210 1 0830 210 2

10:5/16/73 0830 210 2 0800 210 1

11:5/17/73 0800 210 1 0830 210 2

12: 5/18/73 0830 210 2 0800 210 1

13:5/19/73 1300 210 1 1330 210 2

14:5/20/73 0630 213 2 0700 212 1

15:5/21/73 1330 210 1 1300 210 2

36.

Table 3.

Daily Treatment Log

Group II

Subject #7 -- JH Subject #8 -- AH

total totalDay & date start treatment breathing start treatment breathingof bedrest time time system # time time system #

(mins) (mins)

1: 5/8/73 1330 110 1 1300 110 2

2: 5/9/73 1300 151 2 1330 151 1

3: 5/10/73 1330 160 1 1300 160 2

4: 5/11/73 1300 180 2 1330 180 1

5: 5/12/73 1300 210 1 1330 210 2

6: 5/13/73 1330 210 2 1300 210 1

7: 5/14/73 0800 210 1 0830 210 2

8: 5/15/73 1330 210 2 1300 210 1

9: 5/16/73 1300 210 1 1330 210 2

10:5/17/73 1330 210 2 1300 210 1

11:5/18/73 1300 210 1 1330 210 2

12:5/19/73 0830 210 2 0800 210 1

13:5/20/73 1300 210 1 1330 210 2

14:5/21/73 0700 210 2 0630 210 1

15:5/22/73 1300 210 1 1330 210 2

37.

As mentioned earlier, the entire dressing procedure was performedwith the subject supine. When necessary, subjects were log-rolled to one sideof the bed so that the garments could be positioned under them. Unavoidablythe head had to be elevated slightly for donning the bubble helmet. Since thebedrest protocol allowed the subjects to move or elevate their arms, thisfreedom was also allowed during treatments. Occasionally some of the subjectspreferred to support their hands on pillows. Often loose fitting stockingswere worn. Disrobing, from depressurization to complete removal of thegarment, required less than one minute.

Breathing pressure, heart rate, and electrocardiographic patterns(ECG) were recorded continuously throughout each treatment. In addition torecording, ECG's were monitored visually from the screen of a multichanneloscilloscope. ECG signals were detected by small disk electrodes (Beckman)which were located on the wrists and the right foot. This arrangement ofelectrodes produced patterns similar to the standard limb leads and permittedtheir application after the subjects were fully suited. Small preamplifier unitswere located on the beds. The ECG and recording equipment were furnishedby the Human Research Facility. Periodically throughout each treatment suitcounterpressure, blood pressure, and calf circumference measurementswere taken. Calf circumferential (girth) change was used as a simple indexof pooling at different breathing pressures. These data, along with observerand subject comments, were kept in individual log books.

Subjects were visually examined daily as part of the dressing procedureto determine the extent and location of any suit related trauma. Also subjectswere quizzed to determine subjective response to the entire treatment pro-cedure. Generally suit induced traumas were minimal and consisted ofpetecbiae development in the supraclavicular region of the shoulder andoccasionally in the antecubital folds. The petechiae in the first case resultedfrom reduced counterpressure to the area and in the second from fabricpinching with flexion. In no case were the effects alarming or progressive.Most cases were clear by the next treatment day. Fluid infiltration into tissueswas not a problem. Markings on the skin from garment seams and bladderedges, although prominent immediately after undressing, usually cleared in amatter of a few hours after treatment.

Generally the subjects did not find the treatments physically objection-able; however, some compression of the abdominal wall by the bladder at thehighest breathing pressure (100 mm Hg) made breathing difficult. Subjectsquickly learned to produce neck seal leaks during the high pressure phase ofthe treatment in order to drop the pressure transiently to a more comfortablelevel. As a result, rapid pressure excursions from 100mm Hg down to as lowas 20 mm Hg were not uncommon. We did not totally discourage this action,feeling that the type of pressure response produced was in line with the desiredtreatment program and would be good exercise for the vasculature. Pressureequalization in the middle ear did not appear to be a problem.

38.

Various forms of diversionary activities were practiced to assist inthe passage of time during the treatments. Perhaps the most common enter-tainment was color television. The TV was suspended over the bottom of thebeds and angled so that viewing in the horizontal position was not difficult oruncomfortable. Often subjects would sleep or doze for periods of up to 1 houror more. Newspaper reading was also common. Approximately mid-waythrough the 15 days of bed rest, a manually operated TV game (Magnavox) wasobtained. Even though a variety of games requiring two persons could beplayed, interest dwindled after two days. Occasionally candies (Beech-Nut LifeSavers, Inc., New York, N. Y. ) were placed on the helmet microphone boom in aposition accessible to the subject's tongue. Although most of the subjectsenjoyed this treat, the practice was abandoned due to possible interferencewith biochemical test procedures.

RESULTS OF TREATMENT RELATED MEASUREMENTS

A great variety of physical and physiological tests was performed pre-and post-bed rest by several investigators. Basically, the physical test pro-gram was related to detecting decreases in orthostatic tolerance and exercisecapability following bed rest and relating these to the relative effect of theRGG on prevention of the deconditioning process. The physiological testsincluded body composition studies and blood and urine biochemistries. Inaddition, routine metabolic ward data were collected. These tests andmeasurements and their results are to be reported elsewhere. In this reportwe deal only with those tests and measurements performed as part of the RGGtreatment program.

Electrocardiographs and Heart Rate

Electrocardiographic patterns (ECG) were both recorded and visuallydisplayed throughout each treatment session. The principal reason-for moni-toring the ECG's was as an on-line safety measure rather than for post-testanalysis. It is fairly well established that pressure breathing may induce ECGpattern change, e. g. inverted T waves; however, the liklihood was reduced byapplication of torso counterpressure. Also, the bradycardia of impending syn-cope (from overpooling) or apprehensional tachycardia could be detected.

The strip chart ECG's from all of the treatment sessions have beenexamined. Not one example of an inverted T or premature ventricular contrac-tion (PVC) was found. However, a degree of arrhythmia was observed in allsubjects and at all pressures, which, although an R to R interval analysis wasnot made, appears to be greater than normally expected. The phenomenonappears to have been related to normal reflex responses that were accentuated

39.

by the vascular pumping action during the respiratory cycle. The effect ofincreased myocardial storage of catecholamine products was not evidentsince the degree of tachycardia or arrhythmia did not change significantlyduring the 15 days of bedrest. Some shouldering on the descending limb ofthe QRS complex was observed in some of the records. This effect probablyresulted from electrical axis rotation due to the pressure breathing.

Because of the RGG counterpressure gradient, a tachycardia similarto that observed in non-compensated positive pressure breathing was predicted.Ernsting (15) maintains that the magnitude of the increase in heart rate inducedby pressure breathing depends upon the pressure level, the area to whichcounterpressure is applied, and the duration of exposure. Generally, thegreater the pressure the higher the heart rate. The tachycardia probablyresults from reduced effective blood volume concommitant with reduced rightheart filling pressure. If the RGG worked properly, we should have seen anincrease in heart rate when the breathing pressure was at design gradientlevel pressure or above, and a low (or even reduced) rate at the lower breath-ing pressures. In order to determine whether this effect actually did occurduring treatment, heart rates were counted from daily records for all foursubjects. Because the breathing pressure varied, care was taken to selectpoints that were stable. The average of ten counts per subject at each of fourselected breathing pressure levels is plotted in Figure 17. A direct andessentially linear relationship between heart rate and breathing pressure wasfound. Using the mean value for all subjects, the difference between theselected pressure levels was greater with increasing pressure. A summaryof the data is given below:

Breathing pressure level Average HR A HR/level HR range(ind. aver.)

20-39 mmHg 64.5 bpm --- 49.3-75.8 bpm40-59 " 77.1 " 12.6 bpm 61.3-88.6 "60-78 " 94.0 " 16.9 " 76.0-108.0 "80-100 " 117.5 " 23.5 " 93.8-129.4 "

During a single breathing pressure cycle (25 to 100 mm Hg), the averageincrease in heart rate was nearly 53 bpm. Subject #4 was the most labile,showing an increase of 69.2 bpm over the pressure range. There was noevidence of increased ECG irregularities at the higher rates and higherpressures. If the increased rates observed at the higher pressures may beequated to cardiac exercise and if the reduced cardiac loads associated withweightlessness play a role in the deconditioning process, then it is fair to saythat this mechanism should have been favorably affected by the RGG treatments.

40.

BREATHING PRESSURE

LEVELS:

A = 20-39 MM HGB = 40-59 MM HGC = 60-79 MM HGD = 80-100 MM HG

140

SUBJECT #4, D.,S SUBJECT #7, J.H.

SUBJECT #8, AH.-

120

110

100- SUBJECT #1, F.F.

, 90

bU

70

60

50

A B C D A B C D A B C D A B C

BREATHING PRESSURE LEVEL

Figure 17. Effect of breathing pressure on heart rate. (Average of 10 datapoints per subject per breathing pressure level.)

41.

Venous Compliance

Except for one day for each group (day 5, group 1; day 3, group 2),venous compliance measurements were made on both RGG treated and control

subjects every second day of bed rest. The technique and equipment used have

already been described. Since this was the only test of deconditioning doneduring the course of the bed rest, we relied upon it to reflect the degree of

effectiveness of the RGG treatments. If, for example, an increase in compli-

ance was observed after a few days in bed, in both suited and control subjects,

we planned to intensify the treatment program. Unfortunately, however, thisoption did not occur, since significant changes in venous compliance were not

observed in either group. The results of the successive measurements are

plotted in terms of forearm girth change at 60 mm Hg cuff pressure in Fig. 18.

The data show a general tendency for the compliance to decrease

during the first week of bed rest. From the 7th through the 15th day of bed

rest, the values for the treated subjects cycled insignificantly; however, in the

control subjects restoration of first day values occurred in all cases. Except

for the initial decrease, the changes observed were probably within the error

range of the instrument and are not considered significant. These resultsraise a number of questions, the first of which involves the accuracy of the

technique. Because we were aware of possible inaccuracies, we took great

care to check instrument function, calibration, and technique. We found noevidence of problems. We must assume, therefore, that the results obtained

were valid. Why, then, was not an increase in venous compliance observedeven in the control subjects, as would be predicted based upon results obtained

in other weightlessness simulation studies (12)? One possible explanationmay be related to differences in the deconditioning process when bed rest withor without water immersion is used as a simulant. Also, do veins become

"flabby" and more compliant, or stiff and rigid and less compliant, as decon-ditioning progresses? Additional study is needed.

Tests of Garment Function

Tests of garment function including counterpressure measurementsand calf girth measurements were performed during the treatment sessions.Counterpressure measurements were taken to verify the design pressure andgradients, and to determine whether the garment fabric would weaken as theresult of daily donning fatigue (set), or if the original pressure would bediminished by loss of body mass. The technique and device used have alreadybeen described. Counterpressure measurements, always taken on the thighand/or calf, were usually taken daily and recorded in the subject's log book.The results showed that not only were the pressure and gradients well withinthe ± 5 mm Hg design limits, but also that in 15 days of wear the decreases inpressure due either to fabric changes or loss of body mass were minimal forthe areas sampled (the average of 60 measurements was -2mm Hg).

42.

SUBJECT #1, TREATED

4

65 SUBJECT #2, CONTROL

4

- 6 SUBJECT #3, CONTROL

LLJ

SUBJECT A, TREATED

,-

7 SUBJECT #5, CONTROL

U 7_o SUBJECT #6, CONTROL_ 6

:-A

SUBJECT #7, TREATED5

6 SUBJECT #8, TREATED

1ST 3RD 5TH 7TH 9TH 11TH 13TH 15TH

DAY OF BED REST

Figure 18. Venous compliance change over the 15 days of bed rest -- expressedas change in forearm girth at 60 mm Hg occlusion pressure.

43.

Calf girth measurements were made on the treated subjects, using asmall, flexible steel metric tape, several times during the bedrest period.Both nude and over-the-garment circumferences were obtained. The nudemeasurements were directed toward discovery of loss of body mass. Althoughthere was some variation (± 0.5 mm) from day to day in each subject, no pro-gressive decrease in calf girth was detected. The variability could have beendue to measurement error and/or slight changes in the location of the measure-ment. Comparisons of calf circumferences obtained prior to garment construc-tion to those taken during bed rest showed a slight decrease in the latter (anaverage of 0.4 cm), but other indications showed that design counterpressureswere not significantly affected. Except for one subject (#8, AH), who lostnearly 2 kg during the testing period, total body weight changes were notsignificant.

Calf circumference measurements over the garment taken periodicallyduring treatment sessions substantiated the evidence that the RGG was indeedcausing blood to pool in the leg. An increase in girth ranging from 0.5 to0.75 cm was found when early and late individual treatment session measure-ments were compared. These values compare favorably with the increaseobserved when a person goes from lying to standing position. There was somevariability in the measurements associated with the actual elapsed time intothe treatment and the breathing pressure existing at the time of the measure-ment.

Some blood pressure measurements were taken during the treatments,using standard clinical methods. Korotkoff sounds were easily detectable viaa stethoscope applied over the garments. In order to obtain the true correctedblood pressure, one must subtract out the difference between the breathingpressure and the counter pressure applied by the garment to the antecubitalarea. The results of these measur